This invention relates to devices and methods for sharpening saw blades and, in particular, to a mechanism for accurately indexing and profiling the teeth of band saw blades of the type used in lumber mills. The invention has special utility for band saws with variable pitch tooth spacing.
Band saws are used in lumber mills to cut logs into dimensional lumber. Band saw machines use blades that require regular maintenance to eliminate wear. A sharpening operation called xe2x80x9cprofilingxe2x80x9d helps to redefine the profile shape of cutting teeth of the saw blade. Prior-art profiling machines include an indexing mechanism that advances the saw blade into position for sharpening with a grinding wheel that is plunged into a gullet between adjacent teeth of the saw blade to sharpen a cutting face of the tooth. Some prior-art profiling machines then advance the blade and retract the grinding wheel in concert so that a back side of the adjacent tooth is also sharpened. The indexing mechanism and grinding wheel may be driven and timed by a cam assembly or by a CNC controller that operates linear or rotary actuators. In prior-art band saw profiling machines the indexing movement of the blade and the plunging movement of the grinding wheel are regular, requiring minimal set up for most saw blades having a constant pitch. However, newer variable-pitch saw blades have complex tooth spacing patterns, often combined with variable-depth and variable-back angles, that cannot be profiled by prior-art cam-driven machines. CNC-controlled sharpening machines are capable of storing predefined profile programs for variable-pitch saw blades. However, grinding wheel wear, indexing mechanism slip, blade stretch, tolerance stacking, and operator error are all sources of inaccuracy that limit the ability of prior-art machines to sharpen variable-pitch saw blades. Human error in machine setup and slight variations in blade shape are also factors that make it impracticable to implement profiling for variable-pitch saw blades using known machines.
In accordance with the present invention, a band saw profiling machine includes an indexing mechanism having a feed finger mechanically linked to a caliper finger for reciprocating movement therewith. The caliper finger is urged toward the feed finger during an indexing movement of the indexing mechanism to measure the spacing between adjacent teeth of a band saw blade on-the-fly and concurrently with advancement of the saw blade. The tooth spacing measurement is then used in the band saw sharpening machine to provide feedback for a subsequent indexing movement of the indexing mechanism, to accurately position the band saw blade for sharpening of a row of teeth. A grinding wheel is driven under computer control to plunge toward a centerline of the saw blade and grind a cutting face and gullet of a first tooth of the saw blade while the indexing mechanism retracts. The indexing mechanism then begins to advance the saw blade and measure the spacing between another pair of teeth while the grinding wheel grinds the back side of a second tooth of the saw blade adjacent the first tooth.
A control unit of the sharpening machine can accept input of shape factors from an operator that are used to alter the pattern of motion of the indexing mechanism, the grinding wheel, or both.
Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.